IDE Can't Find Serial Port

So I recently just got Arduino, and the software with it, and it was working perfectly fine for the first day.

But now, when I try to upload a program to an Arduino Uno breadboard, it tells me that my COM3 isn't available. I went to my Device Manager, and was able to go to PORTS (COM & LPT) and saw the COM3 port, but for some reason, it doesn't show up in the programming interface when I go to Tool > Port. Any suggestions? (btw I'm new to this so sorry if my terminology is off...)